The present invention relates to a slide bearing for an internal combustion engine having a bearing bore provided in a bearing box, which is contoured in the form of grooved recesses distributed over the axial length and running in a peripheral direction, and provided with a bearing layer forming a running surface for taking up a bearing journal.
Rather than conventional slide bearings with bearing shells set in a bearing box, if slide bearings are used in which the bearing bores in the bearing boxes are coated directly with a bearing layer after an intermediate layer is applied, for bearing the crankshaft of an internal combustion engine in the crank housing or for bearing the crankshaft journal in the connecting rods, the tolerance for the bearing clearance can be reduced due to a range of tolerance for manufacturing the bearing shells to be otherwise considered being omitted here. Because the bearing noise is dependent on the respectively largest bearing clearance, particular significance is given to reduction of the bearing clearance with respect to the formation of noise of these slide bearings and thus diminishing of the range of tolerance decisive for the greatest bearing clearance.
In order to diminish the influence of a hard intermediate layer between the bearing layer and a metallic bearing layer on the durability of a slide bearing in the event of partial wear of the bearing layer, it is known (EP 0 155 257 B2) to provide the surface of the bearing metal layer bearing the intermediate layer with a contour which forms grooves running in a peripheral direction, so that when the running surface, which follows the contour of the bearing metal layer when applied to the intermediate layer, is worn, the intermediate layer penetrating in the vicinity of the running surface cannot form any larger continuous surface areas because with increasing abrasion of the bearing layer the intermediate layer areas lying in the running surface are also worn down, causing the underlying bearing metal layer to be exposed which still ensures adequate slide properties. A requirement for the desired effect is that the intermediate layer be applied to a metal bearing layer and not to a protective steel surface.
Finally, it is known (U.S. Pat. No. 2,187,755 A) to provide the bearing bore of a machine element with a contour in the form of grooved recesses distributed over the axial length and running in a peripheral direction, on which a multilayered bearing layer is deposited galvanically and then partially cut down, creating a smooth, non-profiled bearing surface which displays on its surface alternating areas of different bearing materials. Running surfaces with alternating areas of different bearing materials can improve the bearing conditions with respect to bearing capacity and bearing properties. Such running surfaces with different bearing materials do not however influence noise development.
The object of the present invention is therefore to provide a slide bearing for an internal combustion engine of the type initially described such that a clear reduction in bearing noise can be reckoned on.
The invention solves this task by the fact that the running surface of the bearing layer applied to the bearing bore has a contour with respect to spacing matching the contour of the bearing bore in the form of grooved recesses distributed over the axial length and running in a peripheral direction.
By means of the contour of the running surface in the form of grooved recesses running in a peripheral direction, the minimum bearing clearance to be given for forming a hydrodynamic lubricant wedge can be reduced for lubrication, because the recesses running in a peripheral direction on the one hand produce an additional supply of lubricating oil in the narrowest gap between running surface and journal, and on the other hand the lubricating oil penetrating axially outwards is hindered on both bearing sides. Surprisingly, the operating safety of the slide bearings is not impaired by the profiling of the bearing bore, even though the bearing layer is applied directly or via an intermediate layer as bonding agent or as diffusion barrier on the steel bearing box. Adhering to narrow ranges of tolerance should be decisive for this, as they are possible only when bearing shells are omitted. Due to the narrow ranges of tolerance and reduction of the lower limit for the bearing clearance advantageous provisions for low-noise slide bearings for bearing a crankshaft in a crank housing or a connecting rod on the crankshaft journal can be ensured.
To guarantee adequate operational safety the depth of the grooved recesses is to be limited upwards. Advantageous ratios result when the depth of the grooved recesses corresponds at most to half the thickness of the bearing layer. So that the effect of the grooved recesses running in a peripheral direction on the size of the minimal clearance to be given can be utilized advantageously, the depth of these recesses in a downwards direction can be limited to a fifth of the thickness of the bearing layer.
Because what matters is the maximum bearing clearance with respect to the development of noise of slide bearings according to the present invention, the wear on the bearing layer should be the least possible. For this purpose the bearing layer can display a minimal hardness of 35 HV. The reduced wear of the bearing layer also offers greater operational safety in conjunction with the profiled bearing bore in the steel bearing box.